wip(E4): partial source-pin + non-transitive flip [stdlib E4 attempt-1 WIP checkpoint]

Incomplete WIP from a worker killed at the 55-min wall (large blast radius:
core source-pin + ~8 example migrations + ~10 library module migrations).
Committed so the resumed session continues on a clean tree. May not build.

library/modules/ui/glyph_cache.sx

@@ -1,4 +1,5 @@
 #import "modules/std.sx";
+#import "modules/allocators.sx";
 #import "modules/opengl.sx";
 #import "modules/gpu/types.sx";
 #import "modules/gpu/api.sx";